The FRB–SGR connection

ABSTRACT The discovery that the Galactic Soft Gamma Repeater (SGR) 1935+2154 emitted Fast Radio Burst (FRB) 200428 simultaneous with a gamma-ray flare, demonstrated the common source and association of these phenomena. If FRB radio emission is the result of coherent curvature radiation, the net charge of the radiating ‘bunches’ or waves may be inferred from the radiated fields, independent of the mechanism by which the bunches are produced. A statistical argument indicates that the radiating bunches must have a Lorentz factor ⪆ 10. The observed radiation frequencies indicate that their phase velocity (pattern speed) corresponds to Lorentz factors ⪆ 100. Coulomb repulsion implies that the electrons making up these bunches have yet larger Lorentz factors, limited by their incoherent curvature radiation. These electrons also Compton scatter the soft gamma-rays of the SGR. In FRB 200428, the power they radiated coherently at radio frequencies exceeded that of Compton scattering, but in more luminous SGR outbursts, Compton scattering dominates, precluding the acceleration of energetic electrons. This explains the absence of a FRB associated with the giant 2004 December 27 outburst of SGR 1806−20. SGR with luminosity ≳ 1042 erg s–1 are predicted not to emit FRB, while those of lesser luminosity can do so. ‘Superbursts’ like FRB 200428 are produced when narrowly collimated FRB are aligned with the line of sight; they are unusual, but not rare, and ‘cosmological’ FRB may be superbursts.

Scale-invariance in the repeating fast radio burst 121102

The statistical properties of the repeating fast radio burst FRB 121102 are investigated. We find that the cumulative distributions of fluence, flux density, total energy and waiting time can be well fitted by the bent power law. In addition, the probability density functions of fluctuations of fluence, flux density and total energy well follow the Tsallis q-Gaussian distribution. The q values keep steady around q ∼ 2 for different scale intervals, indicating a scale-invariant structure of the bursts. The statistical properties of FRB 121102 are very similar to that of the soft gamma repeater SGR J1550-5418. The underlying physical implications need to be further investigated.

Statistical properties of magnetar bursts and FRB 121102

ABSTRACT In this paper, we present statistics of soft gamma repeater (SGR) bursts from SGR J1550−5418, SGR 1806−20, and SGR 1900+14 by adding new bursts from Kırmızıbayrak et al. detected with the Rossi X-ray Timing Explorer. We find that the fluence distributions of magnetar bursts are well described by power-law functions with indices 1.84, 1.68, and 1.65 for SGR J1550−5418, SGR 1806−20, and SGR 1900+14, respectively. The duration distributions of magnetar bursts also show power-law forms. Meanwhile, the waiting time distribution can be described by a non-stationary Poisson process with an exponentially growing occurrence rate. These distributive features indicate that magnetar bursts can be regarded as a self-organizing critical process. We also compare these distributions with the repeating fast radio burst (FRB) 121102. The statistical properties of repeating FRB 121102 are similar with magnetar bursts, combining with the large required magnetic field (B ≥ 1014 G) of neutron star for FRB 121102, which indicates that the central engine of FRB 121102 may be a magnetar.